This invention relates to the field of timing methods and in particular, timing synchronization methods.
Timing synchronization issues affect a variety of fields from network communications to manufacturing. In particular, technological applications using multiple electronic devices require some method of synchronizing those devices in order to ensure their proper function. Such systems with multiple devices present difficulties when working with time readings due to the potential for each device's clock to be set to a different time and have differing drift rates. The traditional solution to these problems entail invoking one of many clock synchronization protocols, in which each device participates in an information exchange with the others resulting in each device's clock being set to the same time. In particular, present timing mechanisms for relating time readings from many devices with different clocks require each of the devices to interactively participate in a clock synchronization protocol. Each of the devices is required at some point in the protocol to reset their clocks in response to some received instruction or calculation. As described below, it would be advantageous in many situations to provide a means for obtaining sufficient timing information in a remote sensing application while avoiding clock synchronization entirely.
In remote sensing applications where a large number of sensors will be deployed, cost considerations provide motivation to ensure that each sensor is as simple as possible. Each component of a sensor which can be rendered unnecessary through proper design may represent relatively little cost reduction on a per sensor basis, but significant savings may be realized when this is applied to all the sensors at large. In addition, for sensors without an external power supply, this simplification may improve battery life as well.
For remote sensing applications where communications between the sensors and the central data collection mechanism occur wirelessly, one way to simplify sensors is to eliminate the need for them to receive messages. If the messaging protocol allows the sensors to transmit their data without responding to messages from the central hub, then the cost and power consumption of including a receiver in the hardware can be avoided.
The receiver-free remote sensor design suggested in the preceding paragraph presents two hurdles to implementation. First, if the sensors are only capable of one-way communication, then the central hub has no means for requesting a message to be resent if it is missed due to interference or a collision of transmissions by multiple sensors. Requiring the sensors repeat each of their messages reduces the likelihood of this possibility, but introduces the second hurdle, i.e., the possibility that messages are sequenced incorrectly unless the sensor's clocks are synchronized. However, note that utilizing a traditional clock synchronization algorithm would require the sensors to be able to reset their clocks in response to some instruction or calculation that occurs at some point in the protocol, precluding the elimination of the receiver from the sensor hardware. Accordingly, it would be desirable to provide a system that allows sensors in a remote sensing application the ability to perform the desired message repetition while providing the central data collection hub with the timing information necessary for the hub to reconstruct the correct sequence of messages without necessitating clock synchronization.